The human body GI tract comprises the esophagus, the stomach, the small intestine, the large intestine, the colon, and the anal sphincter and is generally described as having a tract axis. Like other organs of the body, most notably the heart, these organs naturally undergo regular rhythmic contractions. In particular these contractions take the form of peristaltic contractions and are essential for the movement of food through each of the respective organs. Like the heart, these contractions are the result of regular rhythmic electrical depolarizations of the underlying tissue. With regards to the small intestine and large intestine, normal electrical depolarizations (“slow waves”) typically occur at a rate of approximately 15 and 1 beats per minute (bpm) respectively. Similarly, in the stomach, normal slow waves typically occur at a rate approximately 3 bpm. Not all of these depolarizations, however, normally result in a contraction of the organ. Rather contractions occur upon the occurrence of a normal electrical depolarizations followed by a series of high frequency spike activity.
In some individuals, however, either the regular rhythmic peristaltic contractions do not occur or the regular rhythmic electrical depolarizations do not occur or both do not occur. In each of these situations the movement of food may be seriously inhibited or even disabled. Such a condition is often called “gastroparesis” when it occurs in the stomach [30]. Gastroparesis is a chronic gastric motility disorder in which there is delayed gastric emptying of solids or liquids or both.
Symptoms of gastroparesis may range from early satiety and nausea in mild cases to chronic vomiting, dehydration, and nutritional compromise in severe cases. Similar motility disorders occur in the other organs of the GI tract, although by different names.
Diagnosis of gastroparesis is based on demonstration of delayed gastric emptying of a radiolabeled solid meal in the absence of mechanical obstruction. Gastroparesis may occur for a number of reasons. Approximately one third of patients with gastroparesis, however, have no identifiable underlying cause (often called idiopathic gastroparesis). Management of gastroparesis involves four areas: (1) prokinetic drugs, (2) antiemetic drugs, (3) nutritional support, and (4) surgical therapy (in a very small subset of patients.) Gastroparesis is often a chronic, relapsing condition; 80% of patients require maintenance antiemetic and prokinetic therapy and 20% require long-term nutritional supplementation. Other maladies such as tachygastria or bradygastria can also hinder coordinated muscular motor activity of the GI tract, possibly resulting in either stasis or nausea or vomiting or a combination thereof.
The undesired effect of these conditions is a reduced ability or complete failure to efficiently propel intestinal contents down the digestive tract. This results in malassimilation of liquid or food by the absorbing mucosa of the intestinal tract. If this condition is not corrected, malnutrition or even starvation may occur. Moreover nausea or vomiting or both may also occur. Whereas some of these disease states can be corrected by medication or by simple surgery, in most cases treatment with drugs is not adequately effective, and surgery often has intolerable physiologic effects on the body.
For many years, sensing of the peristaltic electrical wave and gastrointestinal stimulation at various sites on or in the GI tract wall of the digestive system or nerves associated therewith have been conducted to diagnose and treat these various conditions. Examples sensing and GI tract stimulation are set forth in commonly assigned U.S. Pat. Nos. 5,507,289, 6,026,326, and 6,216,039, all of which are incorporated herein by reference.
Electrical stimuli are applied from the neurostimulator implantable pulse generator (IPG [50]) through leads and electrodes affixed at sites in the body of the patient or the GI tract wall that permit the electrical stimulus to produce a local contraction of a desired portion of the GI tract. The sites of the GI tract wall comprise the outermost serosa or sub-serosally in the inner, circumferential and longitudinal (and oblique in the case of the stomach) smooth muscle layers referred to as the “muscularis externa”. The smooth muscle is preferably comprised of innervated muscle tissue, and it is theorized that the smooth muscle is neurally electrically stimulated through the nerves associated with and innervating the muscle tissue in order to produce the contraction of the smooth muscle.
An implantable method and system for electrical stimulation of smooth muscle with intact local gastric nerves comprising a portion of the GI tract is disclosed in the '607 patent. The electrical stimulation of the smooth muscle effects local contractions at sites of a portion of the GI tract that are artificially propagated distally therethrough in order to facilitate or aid at least a partial emptying of such portion. This stimulation attempts to create a simulated system that reproduces the spatial and temporal organization of normal gastric electrical activity by creating and controlling local circumferential non-propagated contractions. In this simulated gastric pacing system, each local circumferential contraction is invoked by applying an electrical stimulus to the smooth muscle circumferentially about the portion of the GI tract in a plane substantially perpendicular to the longitudinal axis of the portion. The electrical stimulus is applied at a proximal location and at at least one distal location. The distal location is in axially spaced relationship relative to the proximal location. Further, the applied electrical stimulus is selected to be sufficient to stimulate the smooth muscle to produce the local circumferential contractions at the proximal and distal locations.
The Medtronic® Itrel III® Model 7425 IPG and pairs of the unipolar Model 4300 or Model 4301 or Model 4351 “single pass” leads available from MEDTRONIC, INC., Minneapolis, Minn., have been implanted to provide stimulation to sites in the stomach wall to treat chronic nausea and vomiting associated with gastroparesis. The unipolar electrode of these leads comprises a length of exposed lead conductor and is of the type disclosed in commonly assigned U.S. Pat. Nos. 5,425,751, 5,716,392 and 5,861,014, which are incorporated herein by reference. The above-referenced '039 patent and the '014 patent disclose the Model 4300 lead sewn through the serosa laterally into the muscularis externa to dispose the stimulation/sense electrode therein. A large incision is necessary to access the site, and a needle is used to perforate the serosa and muscularis externa laterally without fully penetrating the wall and to draw the stimulation/sense electrode into the muscularis extema. A laparoscopic approach can be taken, but it is difficult to fixate the lead at the implant site
The stimulation/sense electrodes conventionally employed in such gastrointestinal stimulation systems are formed of bio-compatible material shaped to either bear against the serosa or penetrate sub-serosally into the muscularis externa and polished to present an impervious outer surface. It is also suggested in the above-referenced '014 patent that the exposed electrode(s) of the single pass lead can alternatively be formed of other biocompatible electrode materials, including porous, platinized structures and could feature various pharmaceutical agents. Suggested pharmaceutical agents include dexamethasone sodium phosphate or beclomethasone phosphate in order to minimize the inflammatory response of the tissue to the implanted lead.
When the stimulation leads are inserted or implanted, they are typically anchored in place by sewing the lead through the serosa laterally into the muscularis externa at both the proximal lead entrance site as well as the distal end of the electrode(s). The anchoring is important for the insertion or implantation procedure because this is intended to prevent the stimulation lead from migrating away from a specifically selected stimulation site. The anchoring process is often used during surgical procedures where there is limited space to anchor and secure the lead to tissue, and time constraints to complete the procedure rapidly. For some procedures, anchor the lead to the stomach wall can be one of the most time consuming and invasive portions of the stimulation lead insertion procedure. Clinicians inserting and anchoring therapy delivery elements typically prefer to perform the procedure rapidly, in a minimally invasive manner, and fix the therapy delivery element in a manner that reduces the opportunity for the therapy delivery element to migrate if practicable. Previous stimulation lead anchoring systems can have one or more of the following limitations along with other limitations such as being difficult to use for minimally invasive procedures, difficult to secure the simulation lead in the desired position and susceptibility to lead migration.